SOA Web Service throws 500 Internal Server Error for multiple lines

We have configured SOA web services in our EBS 12.2.10 with database 19c (19.10.0.0.0) system. Web services are being consumed by a vendor for integration purposes for inventory module. Problem we are facing is during sub-inventory transfer for multiple lines, after processing 1st line successfully, EBS does not respond for 2nd line and user at other end receives 500 Internal Server Error. In other words, system is unable to process multiple lines in one go. In service monitor of SOA, I found 2nd line received in system but system could not respond. There is no error details in log. I